TDI "Blow Off Valve"

I did not make this BOV, I don't know how it's made, I don't know where you can get/buy it, and this is not my car.
I do know that a BOV does not make sense on a diesel.
btw. most people that installed this soon took it off because it lets of that sound every time you let off the gas pedal (imagine that on your drive to work).